title: Contractile activity per se induces transcriptional activation of SLC2A4 gene in soleus muscle: involvement of MEF2D, HIF-1a, and TRalpha transcriptional factors.
abstract: Skeletal muscle is a target tissue for approaches that can improve insulin sensitivity in insulin-resistant states. In muscles, glucose uptake is performed by the GLUT-4 protein, which is encoded by the SLC2A4 gene. SLC2A4 gene expression increases in response to conditions that improve insulin sensitivity, including chronic exercise. However, since chronic exercise improves insulin sensitivity, the increased SLC2A4 gene expression could not be clearly attributed to the muscle contractile activity per se and/or to the improved insulin sensitivity. The present study was designed to investigate the role of contractile activity per se in the regulation of SLC2A4 gene expression as well as in the participation of the transcriptional factors myocyte enhancer factor 2D (MEF2D), hypoxia inducible factor 1a (HIF-1a), and thyroid hormone receptor-alpha (TRalpha). The performed in vitro protocol excluded the interference of metabolic, hormonal, and neural effects. The results showed that, in response to 10 min of electrically induced contraction of soleus muscle, an early 40% increase in GLUT-4 mRNA (30 min) occurred, with a subsequent 65% increase (120 min) in GLUT-4 protein content. EMSA and supershift assays revealed that the stimulus rapidly increased the binding activity of MEF2D, HIF-1a, and TRalpha into the SLC2A4 gene promoter. Furthermore, chromatin immunoprecipitation assay confirmed, in native nucleosome, that contraction induced an approximate fourfold (P < 0.01) increase in MEF2D and HIF-1a-binding activity. In conclusion, muscle contraction per se enhances SLC2A4 gene expression and that involves MEF2D, HIF-1a, and TRalpha transcription factor activation. This finding reinforces the importance of physical activity to improve glycemic homeostasis independently of other additional insulin sensitizer approaches.
authors.affiliation: Dept. of Physiology and Biophysics, Institute of Biomedical Sciences, Univ. of Sao Paulo, Av. Prof. Lineu Prestes, 1524, 05508-900 Sao Paulo, Brazil.
authors.forename: Guilherme Alves
authors.initials: GA
authors.lastname: Lima
authors.forename: Gabriel Forato
authors.initials: GF
authors.lastname: Anhê
authors.forename: Gisele
authors.initials: G
authors.lastname: Giannocco
authors.forename: Maria Tereza
authors.initials: MT
authors.lastname: Nunes
authors.forename: Maria Lucia
authors.initials: ML
authors.lastname: Correa-Giannella
authors.forename: Ubiratan Fabres
authors.initials: UF
authors.lastname: Machado
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D051275:Glucose Transporter Type 4 / Q000096:biosynthesis* / Q000235:genetics; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D066298:In Vitro Techniques; D064326:MEF2 Transcription Factors; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D018006:Myogenic Regulatory Factors / Q000378:metabolism* / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D037021:Thyroid Hormone Receptors alpha / Q000378:metabolism*; D015533:Transcriptional Activation / Q000502:physiology*
chemical_list: D051275:Glucose Transporter Type 4; C497444:Hif1a protein, rat; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D064326:MEF2 Transcription Factors; D018006:Myogenic Regulatory Factors; D012333:RNA, Messenger; C495694:Slc2a4 protein, rat; D037021:Thyroid Hormone Receptors alpha